The present invention relates to a keyboard constructed for mechanically encoding the pressing of a key.
Keyboards of the type to which the invention pertains are, for example, constructed to have a plurality of intersecting ducts, channels or guideways holding displacement bodies. The keys are provided with extensions which will be inserted into the two intersecting channels when the respective key is pressed. Thereupon the displacement bodies of one row and of one column of the channel system are displaced and respectively atuate one switch each. This switch actuation constitutes the encoding.
Keyboards of the type referred to above are, for example, disclosed in U.S. Pat. No. 3,845,255. Such a keyboard is particularly comprised of channels with rectangular cross-sections and being filled with balls which serve as displacement bodies. The channels are slightly wider than the diameter of the balls so that these balls can move freely. Each key of the keyboard is, for example, provided with two fingers, pins or arms which respectively lodge in the two channels at an intersection for displacing the balls therein. The displacement distance in each instance is about equal for the width of the respective finger. Switches at the ends of the channels are actuated by and in response to such a displacement.
It was discovered that the keyboards encoded the key depressing incorrectly in some instances, the switches which were closed were sometimes not those which are supposed to be closed. It was discovered that these incorrect switching operations resulted from the following. The various balls are normally retained in the several channels with some slack. As soon as a key is depressed balls are shifted in two channels adjacent to their intersection. Particular balls in these two channels are additionally shifted in and past other intersections. It was found that in some cases these balls are deflected in such an intersection and rather than continuing the longitudinal displacement in the same channel, a ball escapes laterally into an intersecting channel and causes propagation of the displacement into that channel, resulting in an entirely different switch closing. It was found that such erroneous switching will be the more likely the closer the displacement length is to the ball diameter.